View Full Version : Astronauts in space

2003-Oct-20, 05:48 PM
I have heard that astronauts can not stay in space for long periods of time due to gravity. Without gravity, you bones start to weaken, and when you come back into earth's atmosphere, there may be problems with the bone structure . Is this true and if so, can you explain please how.

2003-Oct-21, 04:40 AM
Basically what happens is that astronauts develop osteoporosis when they spend long periods of time in space. On earth, if someone is inactive for long periods of time, the same thing will happen. If we are inactive, our bones loose their density and become brittle. Our bones have developed to allow us to function against the pull of Earth's gravity and we have evolved so that we can walk upright on two legs. In space, those bones (and also muscle) are not used much since the astronauts can float from place to place.

Bones are dynamic, constantly changing. There are three types of cells that help "remodel" the bones constantly. Osteoblasts form new bone. Osteocytes maintain mature bone tissue. Osteoclasts resorb or "eat" older bone tissue.

Living in microgravity reduces the amount of weight that the bones must support to almost zero, and the bones that are usually used in movement are not used. When a bone is not used, a biochemical trigger causes calcium that is normally stored in the bones to be broken down and released into the bloodstream. The exact mechanism that causes the loss of calcium is unknown, but it is believed that microgravity causes the osteoclasts to resorb bone much faster than the osteoblasts create new bone.

The research that is being done on the ISS is very important for the future of human spaceflight. If we are going to send humans to Mars, we need to know how to counteract the effects of microgravity on bones. An astronaut on a 7 month cruise to Mars will loose over 20% of their bone mass, which could result in fractures when the person returns to gravity. A broken hip on Mars would not be good.

In addition, the research will also help in the fight against osteoporosis on Earth. Eight million woman and two million men in the US currently suffer from this disease.

Astronauts and cosmonauts aboard the ISS currently undergo rigorous exercise - about 90 minutes to 2 hours every day, and this seems to help. They ride exercise bikes, run on a treadmill specially designed for space, and simulate weight lifting by pulling on straps. They are also testing dietary supplements to see what works best.

Most astronauts eventually regain their bone mass in time after returning to Earth, but they may not fully recover.

Hope this helps!

2003-Oct-21, 11:38 AM
This is a good question and one which is raised by the public during my observatory lectures.

All that has been said so far is correct, but it goes further, and involves some pretty 'heavy' physiological problems besides bone density loss. The muscles react badly to zero-g, the russians from MIR and SALYUT had to be carried away in stretchers after landing because their legs wouldn't hold them up, muscles deteriorate in zero-g. They did however make a full recovery after 2 weeks so it's not permanent. Your heart becomes weaker in zero-g aswell.

By the way, this problem has a striking similarity to 'deep vein thrombosis' which is the current bane of airlines at the moment.

All this may have an upside because chemists and doctors (specifically EXO-chemists and EXO-biologists) think that they may have a better chance of curing diseases like Aids and some cancers in space because, as any 1st year physics student will tell you, compounds and molecules act 'differently' in a weightless environment.


2003-Oct-21, 01:41 PM
Thanks so much for the replies. They were very detailed answers to my question.